Follow Mackbig's advice. I'll give you the procedure in steps. This is going to be a bit of a project though.
First, get an FTP program. I personally use WS_FTP Pro. It is a paid program and somewhat expensive, but that was mandated by a requirement for SSL connections with the FTP to my web site. There is a dated list of there programs here:
http://www.wurd.com/pwp_ftpindex.php You can probably solict advice from the rest of the gang here as to the best FTP program for you.
Set up the FTP program to access your Comcast personal pages. This might be a sticking point if Comcast doesn't allow FTP access of the pages.
Decide which of your pages you want the flash object to be on and download it. You might need help from the HTML experts here as to how to add the code to your page, e.g. placement wise, etc. Then add the code with notepad or wordpad and save it.
Then upload the revised page back to your web site.
Edit: LOL After reading over this just now, it looks easy peasy, IF you have done it already once.
I'm sure the gang can talk you through the steps though. I edit my site with wordpad, but it is really old school html from '97 (my html books are copyrighted then).